H–He collision-induced satellite in the Lyman α profile of DBA white dwarf stars

Allard, N. F.; Kielkopf, John F.; Xu, Siyi; Guillon, Grégoire; Mehnen, Bilel; Linguerri, Roberto; Mogren, Muneerah Mogren Al; Hochlaf, M.; Hubený, I.

doi:10.1093/mnras/staa707

Cited by 10 publications

(17 citation statements)

References 42 publications

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“…In the following, we use the spectroscopist's notations X, A, B, and C to label the lower adiabatic molecular states of H-He, namely the ground state 1 2 Σ + , the lowest excited states 2 2 Σ + , 1 2 Π, and 3 2 Σ + correlated with H(n=2)+He, while we label the upper states correlated with H(n=4)+He according to their adiabatic ranking in their respective symmetries. For a detailed characterization of states n=2,3, we refer readers to our previ- ous papers (Spiegelman et al 2021;Allard et al 2021) and to earlier literature (Theodorakopoulos et al 1987;Ketterle et al 1985Ketterle et al , 1988Ketterle 1989;Sarpal et al 1991;Lo et al 2006;van Hemert & Peyerimhoff 1991;Ketterle 1990a,b;Allard et al 2020). The molecular states dissociating into 4s, 4p, 4d, and 4f are (7-10) 2 Σ + , (4-6) 2 Π, (2,3) 2 ∆, and 1 2 Φ.…”

Section: Diatomic H-he Potentials and Electronic Transition Dipole Mo...mentioning

confidence: 97%

Collision-induced satellite in the blue wing of the Balmer-beta line and consequences on the Balmer series

Spiegelman,

Allard,

Kielkopf

2022

Preprint

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In this paper we emphasize the non-Lorentzian behavior of the Balmer series in helium-dominated DBA white dwarf stars for which the decades-old problem exists for the determination of the hydrogen abundance. In a very recent work, we have shown that quasimolecular line satellites due to H-He and H-H collisions are responsible for the asymmetrical shape of the Lyman-α lines observed with the Cosmic Origin Spectrograph (COS) and that a similar asymmetry exists for the Balmer-α line profiles. In continuation with very recent work, where the n = 2, 3 potential energies and transition dipole moments from the ground state were determined, here, we present accurate H-He potential energies and electronic transition dipole moments concerning the molecular states correlated with H(n=4)+He and their transition dipole moments with the states correlated with H(n=2)+He. Those new data are used to provide a theoretical investigation of the collisional effects in the blue wing of the Balmer-β line of H perturbed by He. Because of the general trend characterizing the repulsive Σ states of the potential energies involved in the Balmer series, the amplitude in the core of the line is decreasing very fast with the order of the series when the helium density gets as large as 10 21 cm −3 . This study is undertaken by applying a unified theory of spectral line broadening that is valid at very high helium densities found in DZA white dwarf stars. The treatment includes collision-induced (CI) line satellites due to asymptotically forbidden transitions, and it explains the asymmetry observed in their spectra.

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Section: Diatomic H-he Potentials and Electronic Transition Dipole Mo...mentioning

confidence: 97%

Collision-induced satellite in the blue wing of the Balmer-beta line and consequences on the Balmer series

Spiegelman,

Allard,

Kielkopf

2022

Preprint

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“…Figure 1 shows the potential energy curves of the states dissociating into H(n=2)+He and H(n=3)+He. The lowest excited states (n=2) were abundantly discussed by Theodorakopoulos et al (1987), Ketterle et al (1985), Ketterle et al (1988), Brooks & Hunt (1988), Ketterle (1989), van Hemert & Peyerimhoff (1991) , Petsalakis et al (1990), Sarpal et al (1991), Lo et al (2006), Allard et al (2020) and Spiegelman et al (2021).…”

Section: Diatomic H-he Potentials and Electronic Transition Dipole Momentsmentioning

confidence: 99%

“…3 of our preceding paper on the Lymanα line (Spiegelman et al 2021). In that paper we focussed on the medium, long distance, and asymptotic limit of the potential curves, and we were able to solve the uncertainty remaining in Allard et al (2020) involving the adiabatic asymptotic correlation of the Σ states in Lyman-α. The bottom plot of Fig.…”

Section: Collisional Profiles Perturbed By He Atomsmentioning

confidence: 99%

“…The existence of a quasi-molecular line satellite is crucial to understanding the asymmetrical shape of the Lyman-α line observed with the Cosmic Origin Spectograph (COS) on the Hubble Space Telescope (HST) (see Fig. 1 in Allard et al 2020). The resonance broadening of hydrogen perturbed by collisions with H atoms produces asymmetry in the Lyman-α line profile similar to that due to H-He.…”

Section: Introductionmentioning

confidence: 99%

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Collisional effects in the blue wing of the Balmer-α line

Allard

Spiegelman

Kielkopf

et al. 2022

A&A

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In order to investigate the near wing of the Lyman-α line, accurate line profile calculations and molecular data are both required due to the existence of a close line satellite responsible for its asymmetrical shape. Lyman-α lines observed with the Cosmic Origin Spectograph on the Hubble Space Telescope show this peculiarity in the spectra of DBA and DA white dwarf stars. A similar asymmetrical shape in the blue wing can be predicted in the Balmer-α line of H perturbed by He and H atoms. In continuation with a very recent work on the Lyman-α line, where the n = 2 potential energies and transition dipole moments from the ground state were determined, we present new accurate H-He potential energies and electronic transition dipole moments involving the molecular states correlated with H(n = 3)+He and their transition dipole moments with the states correlated with H(n = 2)+He. Those new data and existing molecular data for H(n = 2,3)-H are used to provide a theoretical investigation of the collisional effects in the blue wing of the Balmer-α line of H perturbed by He and H atoms. We note the consequences for the Balmer-α line shape in the physical conditions found in the cool atmosphere of DZA white dwarfs where helium densities may be as high as 1021 cm−3. This study is undertaken with a unified theory of spectral line broadening valid at very high helium densities.

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“…The existence of a quasi-molecular line satellite is crucial for understanding this asymmetrical shape of the Lyman-α line observed with the Cosmic Origin Spectrograph (COS) (see Fig. 1 in Allard et al (2020)). This absorption feature has been predicted by detailed collisional broadening profiles by Allard & Christova (2009).…”

Section: Introductionmentioning

confidence: 99%

Collisional effects in the blue wing of Lyman-alpha

Spiegelman,

Allard,

Kielkopf

2021

Preprint

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Spectral observations below Lyman-α are now obtained with the Cosmic Origin Spectrograph (COS) on the Hubble Space Telescope (HST). It is therefore necessary to provide an accurate treatment of the blue wing of the Lyman-α line that enables correct calculations of radiative transport in DA and DBA white dwarf stars. On the theoretical front, we very recently developed very accurate H-He potential energies for the hydrogen 1s, 2s, and 2p states. Nevertheless, an uncertainty remained about the asymptotic correlation of the Σ states and the electronic dipole transition moments. A similar difficulty occurred in our first calculations for the resonance broadening of hydrogen perturbed by collisions with neutral H atoms. The aim of this paper is twofold. First, we clarify the question of the asymptotic correlation of the Σ states, and we show that relativistic contributions, even very tiny, may need to be accounted for a correct long-range and asymptotic description of the states because of the specific 2s2p Coulomb degeneracy in hydrogen. This effect of relativistic corrections, inducing small splitting of the 2s and 2p states of H, is shown to be important for the Σ-Σ transition dipole moments in H-He and is also discussed in H-H. Second, we use existent (H-H) and newly determined (H-He) accurate potentials and properties to provide a theoretical investigation of the collisional effects on the blue wing of the Lyman-α line of H perturbed by He and H. We study the relative contributions in the blue wing of the H and He atoms according to their relative densities. We finally achieve a comparison with recent COS observations and propose an assignment for a feature centered at 1190 Å.

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H–He collision-induced satellite in the Lyman α profile of DBA white dwarf stars

Cited by 10 publications

References 42 publications

Collision-induced satellite in the blue wing of the Balmer-beta line and consequences on the Balmer series

Collision-induced satellite in the blue wing of the Balmer-beta line and consequences on the Balmer series

Collisional effects in the blue wing of the Balmer-α line

Collisional effects in the blue wing of Lyman-alpha

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